Hippocampus and spatial Hippocampus and spatial memorymemory

A case study of Jon.A case study of Jon.

King, J. A., Trinkler, I., Hartley, T., Vargha-Khadem, F., & Burgess, N. (2004). The Hippocampal Role in Spatial Memory and the Familiarity-Recollection Distinction: A Case Study. Neuropsychology. 18(3), 405-417. [Muriel Delsoin]

Who is Jon?Who is Jon?What does he suffer from?What does he suffer from?

• He is an man who has developmental He is an man who has developmental amnesia, and suffers from perinatal amnesia, and suffers from perinatal anoxia.anoxia.-perinatal anoxia is lack of oxygen to -perinatal anoxia is lack of oxygen to the brain. the brain. http://www.meritcare.com/specialties/rehab/brain/abi/Anoxia/definition.aspxhttp://www.meritcare.com/specialties/rehab/brain/abi/Anoxia/definition.aspx

• His hippocampus is reduced in volume His hippocampus is reduced in volume by 50%. He is impaired in episodic, by 50%. He is impaired in episodic, temporal and spatial memory.temporal and spatial memory.

Jon’s ability to navigate visually was tested using a video game.Duke Nukem (from 3D Realms Entertainment, Dallas, TX)The video game involves moving through a virtual scene, like a town, and shooting enemy forces (aliens).He was a good video game player in general, but his navigation was inaccurate. He was also expected to draw maps in the Speirs, Burgess et al. study and his maps were also inaccurate. - This shows his recollection impairment. - He also could not recognize scenes from the virtual town when such scenes were compared with foils, unlike control subjects who could.

- spatial memory impairment.

Jon’s memory deficits : retrieval of episodic events —comparing memory events’ content with memory context of eventsretrieval of spatial information—comparing memory for object locations from the same view as atpresentation with memory from a shifted viewpoint.Episodic memory test within the VR town:participants follow a path and meeting with virtual characters indifferent places and receiving a different object each time, for atotal of 16 objects. Context-dependent memory for each event (thereceipt of an object) was tested by presenting 2 of the receivedobjects next to a location and a character and asking which objecthad been received in that location or from that character, or whichhad been received first (see Figure 1). Recognition of the familiarityof an object was tested by presenting a received object anda similar looking foil and asking which had previously beenreceived.

  Results:Results:Confirming his impaired episodic memory, Jon performedConfirming his impaired episodic memory, Jon performedat chance on the context-dependent memory questions butat chance on the context-dependent memory questions butwas unimpaired on the object-recognition question (Spiers, Burgess,was unimpaired on the object-recognition question (Spiers, Burgess,et al., 2001).et al., 2001).

• Jon’s spatial memory was investigated:Jon’s spatial memory was investigated:• Used virtual reality paradigm (King et al., 2002). Used virtual reality paradigm (King et al., 2002). • Jon views an array of placeholders, located in a small townJon views an array of placeholders, located in a small town• square, while virtually looking down from the surroundingsquare, while virtually looking down from the surrounding• rooftops. A series of objects appears on random placeholders, rooftops. A series of objects appears on random placeholders, • and then Jon is tested by presenting each object randomly in its and then Jon is tested by presenting each object randomly in its

original location, along with a number of copies of each in foil original location, along with a number of copies of each in foil locations.locations.

• -The task is to identify the one in the correct original location. -The task is to identify the one in the correct original location. Between presentation and testing, Jon either remains in the Between presentation and testing, Jon either remains in the original position or is moved instantly to a new location. The original position or is moved instantly to a new location. The difficulty of a condition can be varied with the number of objects difficulty of a condition can be varied with the number of objects and foils.and foils.

• -Jon using two foil objects at random locations. -Jon using two foil objects at random locations. • Results: Results: • -- showed good performance in the same-view condition for showed good performance in the same-view condition for

short listshort list• lengths, with performance reducing from near ceiling to 50% forlengths, with performance reducing from near ceiling to 50% for• List Length 10 (chance performance would be 33%). In the shifted-List Length 10 (chance performance would be 33%). In the shifted-• view condition, he performed at chance for all list lengthsview condition, he performed at chance for all list lengths• greater than 1. greater than 1.

•Jon’s relative impairment compared to control participants in the shifted-view versus same view conditions was not clear, so researchers tried to reduce control participants’ performance overall, by testing them with five randomly placed foil objects. Now, Jon’s differential deficit at shorter list lengths (4 and 7) became clear: - He performed significantly worse than controls in the shifted-view condition and performed better than them in the same-view condition. Jon’simpaired performance from a shifted view indicates impairedallocentric memory. By contrast, his relatively preserved same viewperformance on short lists could be due to familiarity-basedrecognition using preserved egocentric representations. The size ofthe differential deficit on short lists makes the test a potentiallypowerful indicator of hippocampal damage, given Jon’s generallyspared recognition memory.

It was concluded that: Jon’s deficits in spatial memory (from new viewpoints) show an inability to store object locations in an allocentric framework. A close relationship functioning of episodic and spatial memory exists, in which the hippocampus seems to be involved.

We learn that the hippocampus really is associated with and influences spatial memory.

Question:Question:

• ““Do the processes required by the Do the processes required by the allocentric system relate to the allocentric system relate to the hippocampal contribution to context-hippocampal contribution to context-dependent recognition and episodic dependent recognition and episodic recollection?”recollection?”